From e2d301d28d58db7499d6c623c3e7c6d6948d6e7b Mon Sep 17 00:00:00 2001
From: user <ulgerang@gmail.com>
Date: Mon, 27 Apr 2026 20:33:41 +0900
Subject: [PATCH] ui: auto-detect browser language, re-render dynamic content
 on lang switch

---
 internal/webapp/static/app.js | 37 ++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/internal/webapp/static/app.js b/internal/webapp/static/app.js
index 839506c..a5bba2c 100644
--- a/internal/webapp/static/app.js
+++ b/internal/webapp/static/app.js
@@ -435,6 +435,27 @@ function renderAuth() {
   }
 }
 
+function setLanguage(lang) {
+  localStorage.setItem("tutor_lang", lang);
+  document.documentElement.lang = lang;
+  updateStaticText();
+  document.querySelectorAll(".lang-btn").forEach((btn) => {
+    btn.classList.toggle("is-active", btn.dataset.lang === lang);
+  });
+  if (state.session) renderSession();
+  renderFeedback();
+  renderProgress();
+  renderOntology();
+  renderAssetPrompt();
+  const user = JSON.parse(localStorage.getItem("tutor_user") || "null");
+  const token = localStorage.getItem("tutor_token");
+  if (user && token) {
+    setStatus(t("signedInAs", user.email || user.name));
+  } else {
+    setStatus(t("ready"));
+  }
+}
+
 els.logoutButton.addEventListener("click", () => {
   localStorage.removeItem("tutor_token");
   localStorage.removeItem("tutor_user");
@@ -485,16 +506,18 @@ function escapeHTML(value) {
 document.querySelectorAll(".lang-switch").forEach((group) => {
   group.addEventListener("click", (e) => {
     if (!e.target.dataset.lang) return;
-    const lang = e.target.dataset.lang;
-    localStorage.setItem("tutor_lang", lang);
-    document.documentElement.lang = lang;
-    updateStaticText();
-    document.querySelectorAll(".lang-btn").forEach((btn) => {
-      btn.classList.toggle("is-active", btn.dataset.lang === lang);
-    });
+    setLanguage(e.target.dataset.lang);
   });
 });
 
+if (!localStorage.getItem("tutor_lang")) {
+  const browserLang = navigator.language || navigator.userLanguage || "";
+  const lang = browserLang.toLowerCase().startsWith("ko") ? "ko" : "en";
+  localStorage.setItem("tutor_lang", lang);
+  document.documentElement.lang = lang;
+}
+
 updateStaticText();
 window.renderAuth = renderAuth;
+window.setLanguage = setLanguage;
 renderAuth();